Method of producing magnetic disk

ABSTRACT

A method of producing a magnetic disk by lapping a magnetic disk medium, comprising the steps of: preparing a lapping tape having an abrasive particle layer provided with abrasive particle clusters and chip pockets formed between adjacent two clusters, each of said clusters having abrasive particles of Al 2  O 3  or SiC and abrasive particles of diamond, lapping the surface of said magnetic disk medium by using the thus prepared lapping tape.

This is a continuation of application Ser. No. 935,336, filed Nov. 26,1986, now U.S. Pat No. 4,762,534.

BACKGROUND OF THE INVENTION

The present invention relates to a method of producing a magnetic disk,and more particularly to a method of producing a magnetic disk whichmethod uses a lapping tape suitable for lapping the surface of amagnetic disk containing hard fillers (such as particles of Al₂ 0₃, SiC,or the like).

With the recent increase in the recording density of a magnetic disk, ithas become increasingly important to reduce, as much as possible, thedistance between a magnetic head and the surface of a magnetic disk,namely the amount by which the head floats above the surface of thedisk. For this reason, it is required to minimize the roughness of thesurface of the magnetic disk. In order to lap the surface of magneticdisk medium so as to minimize the surface roughness, the surface ismoved while the lapping tape is forced onto the surface.

In producing magnetic disks, the following are some examples ofconventional methods known in the art employing lapping tape: the methoddisclosed in Japanese Unexamined Patent Publication No. 56-130834 inwhich the surface of lapping tape is previously coated with lubricant,the tape being used to lap after it has been dried at a temperaturebetween 30 to 50° C.; and the method disclosed in Japanese UnexaminedPatent Publication No. 56-130836 in which a magnetic disk is preparedwhich has a magnetic film formed on a substrate and having a largesurface-roughness occurring by a binder of thermosetting resin such asepoxy resin, phenolic resin, or melamine resin, and by fillers such asalumina powder, and the thus prepared magnetic disk is lapped whilebeing moved relative to a magnetic head on which a lapping tapeimpregnated with a lubricant such as fluorocarbon is mounted.

The conventional lapping tape on which abrasive particles of Al₂ 0₃, SiCor the like are provided is insufficient to adequately cut protrusionsor heads occurring by fillers protruding from the surface of themagnetic medium when used in lapping the surface of the medium in whichsuch fillers (particles of Al₂ 0₃ having a particle size of 0.5 to 1.3μm) are contained as a durability-and-strength increasing agent, so thatthe conventional lapping tape is impossible to reduce the distance bywhich a magnetic head floats above the surface. On the other hand, withthe type of a lapping tape incorporating abrasive particles of diamondwhich have an improved ability to cut the protrusions caused by fillers,the following problems have occurred. Namely, when the proportion ofabrasive particles contained in a lapping tape is low, the resultingmagnetic medium surface lapped by the lapping tape will have a lot offlaws caused as a result of the lapping working. Conversely, when theproportion of abrasive particles adopted is sufficient for the formationof chip pockets which can prevent the flaws from being caused, theexpense would be too high for mass production of the magnetic disk.

SUMMARY OF THE INVENTION

An object of the present invention is to improve the problems of theprior art and to provide a method of producing a magnetic disk employinga lapping tape which, when employed to lap the surface of a magneticrecording medium, exhibits an ability to cut protrusions formed byfillers protruding from the surface of the magnetic recording medium inan adequate degree without causing thereon any flaws which are apt tooccur in the lapping working.

In order to achieve the above object, the present invention provides amethod of producing a magnetic disk in which the surface of a magneticdisk medium is lapped by means of lapping tape provided with abrasiveparticles of Al₂ 0₃ or SiC, binder resin, and a polyester film, themethod comprising the steps of: preparing a lapping tape having anabrasive particle layer in which abrasive particles of diamond aredispersed in each of abrasive particle clusters formed of either Al₂ 0₃abrasive particles or SiC abrasive particles, which layer has chippockets provided between two adjacent clusters of said abrasiveparticle; and lapping the surface of said magnetic disk medium by makinguse of the thus prepared lapping tape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation showing the surface portion oflapping tape employed in a method of the present invention;

FIG. 2 is a schematic view showing an enlarged part of the lapping tapeshown in FIG. 1;

FIG. 3 is a schematic view showing a partial section of the lappingtape;

FIG. 4 is a block diagram showing the process of manufacturing thelapping tape;

FIGS. 5A and 5B are perspective views showing the states in which amagnetic disk medium is lapped; and

FIGS. 6 and 7 are graphs showing the roughness of the surface of themagnetic disk obtained by the method of the present invention incomparison with a conventional method.

PREFERRED EMBODIMENT OF THE INVENTION

An embodiment of the invention will now be described in detail withreference to the accompanying drawings.

In this embodiment, the proportion of abrasive particles which issuitable for obtaining the required properties of the lapping tape, i.e.the abrasive particle content which is necessary to form chip pockets soas to prevent flaws from occurring, is set to a value between 50 to 90%by weight with respect to the total weight of the abrasive layer, whichabrasive layer consists of: 40 to 89% by weight Al₂ 0₃ abrasiveparticles or SiC abrasive particles; 1 to 10% by weight diamond abrasiveparticles which have a high degree of ability to cut fillers; and theremainder binder resin. By thus setting the composition of and theproportion of abrasive particles, it is possible to obtain lapping tapewhich has the ability to cut the heads of the fillers protruding fromthe surface of the magnetic disk medium in an adequate degree withoutcausing flaws on the surface of the magnetic disk.

The lapping tape employed in the method of the invention has an abrasivelayer schematically shown in FIGS. 1 and 2, which has a plurality ofabrasive particle clusters 1, and chip pockets 2 provided between twoadjacent clusters of the abrasive particle. The abrasive particleclusters 1 are each formed of: abrasive particles 3 of Al₂ 0₃ or SiChaving a mean particle size of 2 to 9 μm; diamond abrasive particles 4having a mean particle size of 1 to 9 μm dispersed in each of theabrasive particle clusters 1; and a binder resin 5 used in the abrasivelayer for bonding the abrasive particles. Referring to FIG. 3, asubstrate 6 of the tape is formed of a polyester film having a thicknessof about 25 μm, and the abrasive layer 7 thereof has a thickness ofabout 15 μm. The abrasive layer 7 consists of: 40 to 89% by weight Al₂0₃ or SiC abrasive particles; 1 to 10% by weight diamond abrasiveparticles; and the remainder binder resin. Preferably, the layer 7should include 60 to 80% by weight Al₂ 0₃ or SiC abrasive particleshaving a mean particle size of about 3 μm, and 2 to 8% by weight diamondabrasive particles having a mean particle size of about 3 μm.

As shown in FIG. 1, the provision of the chip pockets 2 having an arearatio of 15 to 30% regarding the whole surface area of the abrasivelayer which chip pockets exist between adjacent ones of the abrasiveparticle clusters 1 is a requisite for obtaining a lapped magnetic diskproduct with a high degree of precision and without any flaws. In orderto form this desired structure of the abrasive particle clustersprovided with the chip pockets, a high abrasive particle proportion of50 to 90% by weight is needed. If this high proportion is to be composedsolely of the diamond abrasive particles 4 having a high degree ofcutting ability, the expense would be too high for mass production.Therefore, in this embodiment of the invention, a structure is adoptedin which the main part of the structure of the abrasive particleclusters including the chip pockets 2 is formed of abrasive particles ofAl₂ 0₃ or SiC in which diamond abrasive particles 4 are dispersed,thereby obtaining lapping tape which is capable of cutting the heads offillers protruding from the surface of the disk medium without causingflaws. In this case, it is preferred that each of the chip pockets has asize of 10-100 μm. Thus, the most important features of the presentinvention comprise the following three points: (a) the material for theabrasive particle layer of the lapping tape includes 40 to 89% by weightAl₂ 0₃ abrasive particles or SiC abrasive particles which form a mainpart of abrasive particle clusters between adjacent ones of which thechip pockets are provided; (b) the material further includes 1 to 10% byweight diamond abrasive particles which are dispersed in each of theabrasive particle clusters; and (c) the lapping tape is prepared byusing the above material, and the magnetic disk is lapped by use of thethus prepared lapping tape so that there is obtained a surface roughnessregarding the surface of the thus lapped magnetic disk which roughnessensures that, when the resultant disk is rotated with a detecting headfloating 0.14 to 0.19 μm above the surface of the disk, a number oftimes regarding collision occurring between the detecting head and thefillers becomes substantially zero. This z distance of 0.14 to 0.19 μmis called the height for ensuring magnetic head floating.

FIG. 4 shows a specific manner of preparing the lapping tape.

As will be seen from FIG. 4, a lapping tape for use in the method of theinvention is prepared in the following manner in accordance with thisembodiment: A polyester film having a thickness of about 25 μm cleanedfor use was prepared as the substrate of the tape. An abrasive mixtureincluding Al₂ 0₃ or SiC abrasive particles having the mean particle sizeof 2 to 9 μm, diamond abrasive particles having the mean particle sizeof 1 to 9 μm, and binder resin of urethane resin was prepared, and theabrasive mixture was then filtered through a filter of 2000 to 6000mesh. The filtered abrasive mixture was then coated onto the polyesterfilm (Mylar) in a thickness of about 15 μm, and then dried, therebyobtaining the lapping tape employed in the method of the invention. Thechip pockets are holes wherein no substance is present, and they areformed as recesses between two adjacent clusters of abrasive particlesduring the drying process of the abrasive mixture. If lapping isconducted by using a lapping tape with an abrasive layer having no chippocket or chip pocket having an area ratio of less than 15% regardingthe whole area of the layer, powder resulting from the cutting operationis apt to adhere onto the surface of a lapped disk or is apt to adhereto the abrasive particles, thus resulting in an increase in friction. Onthe other hand, when a lapping tape is used which has an abrasive layerhaving abrasive particle cluster and chip pockets, the powder is able toenter the chip pockets, thus it becomes possible to obtain a high degreeof precision or improved surface roughness regarding the lapped surface.In brief, the chip pockets provide an escape route for the powder. Asmentioned above, another important feature of the invention is theaddition of diamond abrasive particles in a small amount.

By using the lapping tape having the structure shown in FIGS. 1 and 2,the surface of a magnetic disk 11 was lapped by subjecting the same to afirst working A and subsequently to a second working B, which arerespectively shown in FIGS. 5A and 5B. First, as shown in FIG. 5A, thefollowing lapping was conducted: a lapping tape 12 (the abrasive layer 7of which includes 73% by weight Al₂ 0₃ abrasive particles having a meanparticle size of 3 μm, and the remainder binder resin) was forced ontothe surface of the magnetic disk medium 11 through a roller 13 withforce of 6 gf while moving at a running speed of 500 mm per min., andsimultaneously the disk medium 11 was rotated at a rotational speed of100 rpm, thereby lapping the surface of the disc medium 11 for 70 sec.while supplying a grinding fluid 16 thereto (working A). Subsequently,as shown in FIG. 5B, the following lapping was conducted: a lapping tape14 (the abrasive layer 7 of which includes 60% by weight Al₂ 0₃ abrasiveparticles having a mean particle size of 3 μm, 5% by weight diamondabrasive particles having a mean particle size of 3 μm, and theremainder binder resin) was forced on the surface of the magnetic diskmedium 11 which had been prepared by the lapping effected in the workingA, through a roller 15 with force of 70 gf while the tape was moving ata running speed of 250 mm per min., and simultaneously the disc medium11 was rotated at a rotational speed of 500 rpm, while at the same timethe roller 15 and the tape 14 were moved in the radial direction at amovement speed of 150 mm per min, thereby lapping the surface of thedisk medium disc 11 for a period of time during which the roller 15 andthe tape 14 make one or two reciprocating movements in a radialdirection (working B). By this working A and the subsequent working B,it was made possible to cut the heads of the filler protruding from thesurface of the magnetic disk medium in an adequate degree withoutcausing flaws, thereby enabling a reduction in the roughness of thesurface of the magnetic disk. Consequently, it became possible to reducethe height for ensuring the magnetic head floating which was about 0.25μm in the prior art to a value of 0.14 to 0.19 μm regarding a magneticdisk produced in accordance with the invention.

FIGS. 6 and 7 are graphs showing the difference between the roughness ofthe surface of magnetic disks A and B produced by the method of theinvention including the lapping process shown in FIGS. 5A and 5B andthat of a magnetic disk (hereinafter referred to as "the comparativedisk") produced by a conventional method. In production of thecomparative magnetic disk, lapping tapes including no diamond abrasiveparticles were used for conducting both the workings A and B to lap thesurface of the comparative magnetic disk. On the other hand, themagnetic disk A of the invention was lapped in the following manner: inthe working A, a lapping tape including no diamond abrasive particleswas used in the same manner as in the lapping of the comparativemagnetic disk, while another lapping tape including 5% by weight diamondabrasive particles was used in the lapping work B in such a first mannerthat this lapping tape was reciprocally moved in the radial direction ofa magnetic disk one time in a case of Example A. In addition, anothermagnetic disk B of the invention was lapped in the work B in such asecond manner that the lapping tape is reciprocally moved in the radialdirection two times in a case of Example B. In FIGS. 6 and 7, thesymbols Ra and Rp indicate the roughness of the surface of the resultantmagnetic disks. Ra is the Center Line Average which is the arithmeticalvalue of all distance of the roughness profile from its center line,while Rp is Levelling Depth which is the vertical distance between thehighest point and the center line of the roughness profile R within themeasured length. From FIGS. 6 and 7, it is clearly seen that thesurfaces of the magnetic disks A and B produced by the method of theinvention possess roughness values which are smaller than those of thecomparative magnetic disk produced by the conventional method using theconventional tape.

As described above, according to the present invention, since thelapping process for lapping the surface of a magnetic disk medium can beperformed by using a lapping tape which is capable of sufficientlycutting the heads of fillers protruding from the surface of the magneticmedium without causing flaws, it becomes possible to provide an improvedroughness for the surface of the magnetic disk, thus enabling to reducea value regarding the height for ensuring magnetic head floating and toenhance the recording density of a magnetic disk.

What is claimed is:
 1. A lapping tape comprising:a substrate made of atape of plastics; an abrasive layer provided on the substrate and havingabrasive particle clusters and chip pockets having an area of 15 to 30%of the entire surface of said abrasive layer formed between adjacent twoclusters, each of said clusters having 40 to 89% by weight abrasiveparticles of Al₂ 0₃ or SiC, abrasive particles of 1 to 10% by weightdiamond and a binder resin bonding these abrasive particles to eachother.
 2. A lapping tape as claimed in claim 1, wherein said abrasivelayer of said lapping tape comprises: 40 to 89% by weight Al₂ 0₃abrasive particles or SiC abrasive particles; 1 to 10% by weight diamondabrasive particles; and the remainder binder resin while the totalweight of these abrasive particles is 50 to 90%, the mean particle sizeof said Al₂ 0₃ abrasive particles or said SiC abrasive particles being 2to 9μ, the mean particle size of said diamond abrasive particles being 1to 9 μm.
 3. a lapping tape as claimed in claim 1, wherein said chippockets have an area of 15 to 30% of the entire area of said abrasivelayer provided on the surface of said lapping tape, and each of saidchip pockets has a size of 10 to 100 μm.
 4. A lapping tape according toclaim 1, wherein said substrate is made of a polyester film.
 5. Alapping tape according to claim 4, wherein said polyester film has athickness of about 25 μm.